Always nice to see someone pushing for bare-metal. I haven't used STM32 myself, but its always a popular choice for beginners. I'd get into it eventually.

I believe STM32 is famous for having the "widest-range ARM cores", from cheap under $1 STM32C0, to ultra-low-power STM32U5, to higher end STM32H7. ST advertises 1290 microcontrollers in their 32-bit ARM family, meaning you almost certainly have some STM32 available that matches whatever project you're trying to do.

For those who need a bit more help, the STM32 NUCLEO boards are a $10 to $15 set of demo-boards / reference designs that help people get started. Many STM32 chips are available in a NUCLEO board, and many boards (not all) have Arduino shield layouts, so the STM32 can be used as a higher-performance Arduino.

Its a good and popular line.